Multiple frequency automatic tuning device



Feb. 13, 1951 A. E. VIOLET 2,541,128

MULTIPLE FREQUENCY AUTOMATIC TUNING DEVICE Filed Nov. 18. 1948 2Sheet,s--Shee+v 1 A WV V U BNVIENTOR ND/ P5 E. 1//0.LET

Feb. 13, 1951 A. E. VIOLET 2,541,128

MULTIPLE FREQUENCY AUTOMATIC TUNING DEVICE Filed Nov. 18, 1948 2Sheets-Shee+v 2 WVENTOR mwme 15. P704157" Patented Feb. 13, 1951MULTIPLE FREQUENCY AUTOMATIC TUNING DEVICE Andi- Emile Violet,Boulogne-Billancourt, France,

assignor to International Standard Electric Corporation, New York, N.Y., a corporation of Delaware Application November 18, 1948, Serial No.60,681

1 In France November 21, 1947 1 4 Claims.

The present invention relates to automatic tuning devices and moreparticularly to such devices used in radio receivers of thesuper-heterodyne type, for example, in the case of carrier shifttelegraph signals.

in the case of frequency modulated telegraph signals, a continuous waveis successively transmitted at two different frequencies, one of whichcorresponding to the marking position and the other one to the spacingcondition. ,In this type of transmission it is of the greatestimportance that the receiver be properly stabilised and that the tuningbe exact otherwise the signals, when they are detected by adiscriminator, may comprise a large D. C. component which may preventthe correct operation of the amplifier tube which follows thediscriminator.

It is possible to overcome this difficulty by eliminating the D. C.component by means of a condenser, but in this case the stability ofoperation is impaired when the transmitter remains for some time on itsspacing or rest position, small impulses are then sufiicient foroperati. g the telegraph relay.

It is also possible to use the D. C. component of the discriminator toreact on the frequency of the local tuning oscillator by means, forinstance, of a reactance tube or variable impedance tube for controllingthe rotation of a motor driving a variable condens r for retuning thereceiving. In practice, the potential supplied by the discrimin torvaries continuously between two potentials corresponding to the markingand spacing frequencies and it is not possible to have a stableoperation. In particular a long spacing signal has the efiect ofcompletely upsetting the operation of the oscillator.

Gne object of the present invention is to provide an automatic tuningcontrol device for frequency modulation receivers, which ensurescomplete stability of operation.

. ccording to one feature of the invention, two -minators are used,respectively tuned on the uency of spacing and marking position. The C.potentials from these discriminators are added and constitute thecontrol potential of the automatic control arrangement.

The above and other features and objects of this invention will becomemore apparent, and

f vention itself, though not necessarly deed by said features andobject, will be best untooo 3y reference to the following description.of an embodiment of the inventiontaken in conjunction with theaccompanying drawings wherein Figs. 1, 2, 3, and 4 are diagrams usefulfor the understanding of the invention, and

Figs. 5 and 6 show schematically preferred embodiments of the invention.

Referring to the drawings, Figs. 1, 2 and 3 represent an incoming waveof constant ampli tude and in which the time is given in the aboissaalong axis xy.

Let us consider a wave which, within a time interval T, passes from afrequency f1 transmitted during a time interval t, to a frequency f2transmitted during a time interval Tt.

' If this wave is considered as a signal wave -frequency modulated byrectangular shaped signals, its analysis in the frequency spectrumrapidly becomes impossible, but it may be considered as the result ofthe superimposition of two waves which are amplitude modulated by arectangular signal; One of these waves has a frequency 11 and a durationt (Fig. 2), the other one a frequency is and a duration l"-t (Fig. 3). i

If the incomin wave is represented in this way, it may be seen thatthere is no reason why one should obtain a wave with a frequency equalto the mean arithmetical value of the component frequencies f1 and is;it also follows that at least one wave of frequency T1 or ii, andgenerally two waves of frequencies f1 and f2 are obtained, which will becalled secondary carrier waves. On the other hand the side bands (notshown on the diagram) relating to each secondary carrier wave aresymmetrical with respect to each secondary carrier wave.

Applicant has found that automatic control of the tuning can be effectedby means of two discriminators tuned respectively on each carrier wave.These discriminators must be sufliciently selective to avoid overdappingof the characteristic potential curves in function of the frequency.

4 shows the response curve of such an arrangement. The output potentialis given i ordinates OV and the frequency in abscissa Of. The left handside of the graph shows the characteristic curve of the firstdiscriminator tuned to frequency f1 and the right hand side of the graphthe characteristic of the second discriminator tuned to frequency is. Itis seen that the detected potentials supplied by the discriminators arenot superimposed if their selectivity is sufficiently high.

5 shows by way of example a preferred embodiment of an automatic controldevice incorporating features of the invention. This device comprisestwo conventional discriminators l and 2. Each of these discriminatorsland 2 comprises two rectifiers such as 3 and 3 which may be doublediode vacuum tubes or dry rectifiers.

The received signals are amplified to an appropriate level (byamplifiers not shown) and applied to conductor 4. The plates of vacuumtube 3 of the first discriminator are respectively connected to one endof the tuned circuits 5 and 6. The resonant circuit 5 is tuned to afrequency slightly below the nominal receiving frequency ii of the firstdiscriminator V(]11) and the second resonant circuit 6 is tuned to afrequency slightly above this same nominal frequency f1 (fl-H1).

The second discriminator 2 is similar to the first one and alsocomprises two resonating circuits 1 and 8 coupled to tube 3' andrespectively tuned above and below the nominal receiving frequency in,i. e. (f2e2) and (f2+ez).

Low pass filters 9 and 9' with relatively high time constants areconnected in the output of the discriminators to eliminate the highfrequency current, and resistances IB having high values are connectedin the output circuit of discriminators I and 2.

Discriminator l is tuned to frequencies (fie1) and (fi-l-ei) deliversbetween terminal 5! and the ground l2 a D. C. potential V1, whoseamplitude depends on the difference between the tuning frequency ii ofthe discriminator and the secondary carrier F1 of the transmitter at thetime. In the same manner, the discriminator 2, whose tuning frequenciesare (f2--2) for the resonating circuit 1 and (fz+e2) for resonatingcircuit 3 delivers between terminal l3 and the ground I l a D. C.potential V2 whose amplitude also depends on the difference between thetuningfrequency f2 of discriminator 2 and the secondary carrier wave F2of the transmitter at that time. This difference in tuning issubstantially the same as that between T1 and F1 if the differencebetween the tuning of the two discriminators corresponds to thedifference in the transmitted frequency. These two potentials are partlyadded and the resulting potential has an amplitude which is collected atpoint l5. This amplitude V depends only slightly on t and Tt. It remainsthe same even if the transmitted wave remains stance a motor l6 by meansof a device I! which may comprise vacuum tubes.

The motor may drive the mobile plates of a tuning condenser 13 in such away as to retune the circuit on the carrier wave. The condenser 18 isconnected to the local oscillator IQ of the receiver shown in blockform. The local oscillator is coupled to detector 20 shown in blockform.

Fig. 6 shows another tuning device. In this case the potential from leadl5 of Fig. 5 is applied to-the grid 2| of a variable reactance vacuumtube 22. The reactance of this tube varies according to the potentialapplied to its grid 2!, and alters the tuning of the resonating circuit23.

The vacuum tube 24 operates as a conventional oscillator. The highpotential is applied in 25 to the anodes of tubes 22 and 24. Theoscillations are transmitted at 26 to the frequency changer stage of thereceiver (not shown) by means of a condenser 21. The connection is madein such away thatthe voltage fluctuations from It result 4 in acorresponding drift in the receiver frequency to adjust it on thefrequency of the receiver.

While I have described a particular embodiment of my invention forpurposes of illustration it should be understood that variousmodifications and adaptations thereof may be made within the spirit ofthe invention as set forth in the appended claims.

What is claimed is:

1. Signal receiving means for successively receiving two differentfrequencies comprising tuning means resonant at said frequencies, afirst discriminator tuned to frequencies lying either side of theoperating range of the first of said different frequencies, a seconddiscriminator tuned to frequencies lying either side of the operatingrange of the other of the second of said different frequencies, means tocombine the output of said discriminators and means to apply thecombined output of said discriminators to said tuning means whereby saidreceiving means is automatically kept substantially in resonance withsaid two different frequencies.

2. Signal receiving means as claimed in claim 1, wherein said firstdiscriminator comprises a full-wave rectifier device, a first pair ofresonant circuits respectively coupled to different halves of saiddevice, each of said circuits adapted to resonate respectively atfrequencies above and below the operating range of one of said differentfrequencies, said second discriminator comprises a full-wave rectifierdevice, a second pair of resonant circuits respectively coupled todifferent halves of said second device, each of said lastnamed circuitsadapted to resonate respectively at frequencies above and below theoperating range of the other of said different frequencies, a pair oflow pass filters having arelatively high time-constant, each connectedacross a different one of said discriminators, and said means to combinethe output of said discriminators comprises'a pair of resistancesserially connected between each other and the output of each of saidfilters, whereby a voltage may be derived at the junction point of saidresistances.

V 3. Signal receiving means as claimed in claim 1 wherein said tuningmeans comprises a variable condenser and a reversible electric motorcoupled to the shaft of said condenser, said motor connected to saidoutput combining means, whereby said motor is driven in either directionin accordance with the potentials derived from said combining means.

4. Signal receiving means as claimed in claim 1, wherein said tuningmeans comprises a local heterodyne oscillator, said oscillator having atuning resonating circuit, a variable reactance electron discharge tubein shunt with said tank. said tube having a control electrode, a cathodeand an anode, the control grid of said tube connected to saidoutputcombining means, whereby the reactance of said resonating circuitisvaried in accordance with the potentials derived from said combiningmeans. 7

ANDRE: EMILE VIOLET.

REFERENCES CITED The following references are of record in the fileofthis patent:

UNITED STATES PATENTS Number Name 7 Date 2,147,509 Wilkens Feb. 14, 19392,393,400 Noviks et al Jan. 22, 1946

